Cold hardiness & minimum temperature

Is grass-leaved bladderwort (Utricularia graminifolia)cold hardy? Hardiness zone & min temp

Also called grass-leaved bladderwort, UG, grassleaf bladderwort.

More about grass-leaved bladderwort

About grass-leaved bladderwort

Utricularia graminifolia · also called grass-leaved bladderwort, UG · houseplant

Utricularia graminifolia is a prized aquatic carnivore from Southeast Asia and South Asia, used in aquascaping as a vivid green foreground carpet plant. It produces fine grass-like leaves that spread into a dense emerald mat, occasionally sending up delicate purple flowers. Demanding in CO2 and light, it rewards advanced growers with one of aquascaping's most striking effects.

Cold limit: USDA 10-12 · RHS H1a (18–25°C)

What grass-leaved bladderwort's hardiness rating actually means

grass-leaved bladderwort is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1a means: Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever. On the US scale that maps to USDA 10-12 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly above about 15 °C (warm, never cold). grass-leaved bladderwort has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for grass-leaved bladderwort as it gets too cold:

Below about above about 15 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can grass-leaved bladderwort go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above above 15 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when grass-leaved bladderwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1a figure above.

grass-leaved bladderwort hardiness — frequently asked questions

Is grass-leaved bladderwort cold hardy?

grass-leaved bladderwort is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. grass-leaved bladderwort can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature grass-leaved bladderwort can survive?

Minimum survivable temperature is roughly above about 15 °C (warm, never cold). grass-leaved bladderwort has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is grass-leaved bladderwort?

grass-leaved bladderwort is rated USDA 10-12 and RHS H1a — Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever.

Can grass-leaved bladderwort survive winter outside?

It can holiday outdoors in summer once nights are reliably above above 15 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to grass-leaved bladderwort below its minimum temperature?

Below about above about 15 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.